Underground storage



- 'July 28,1959 1...,P. MEADE lmnERGRouND STORAGE Filed Nav. 21. i955 INVENTUR.

L. P. MEADE ATTO NE KS United states Paf-em o UNDERGROUND STORAGE Leonard P. Meade, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware Application November 21, 1955, Serial No. 547,964

4 Claims. (Cl. 62`54) This invention relates to underground storage.

In accordance with this invention, a portion of the vapors are continuously or intermittently withdrawn from the cavern, compressed, condensed and returned to the cavern. The return of the condensed material to the cavern dissolves a portion of the more Volatile components in the vapor space, thus reducing the cavern pressure, as does the refrigeration effect produced by the vaporization and condensation cycle. Preferably and advantageously, at least a portion of tlhe more volatile materials, such as ethane, methane and the like, can be separated from the condensed material and diverted from the underground storage system. For example, these light materials can be used as fuel.v This results in a further lowering of the pressure within the cavern.

By the practice of the invention, itis possible to reduce the cavern pressure to a point where it is substantially equal to the formation pressure. Formation pressure is the static pressure exerted by natural fluids in the formation. Under these circumstances, surface tension of the water in the formation effectively prevents ow of stored material out of the cavern or flow of fluids from the surrounding formations into the cavern.

Accordingly, it is an object of the invention to provide Y a system for operating an underground storage cavern at a reduced pressure.

It is a further object to provide a system for continuously or intermittently separating more volatile components from the vapors present in the cavern.

lt is a further object to provide a simple, economical and `eicient method of operating an underground storage installation.

Various other objects, advantages and features of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawing, in which:

The figure is a schematic flow diagram of an underground storage system constructed in accordance with the invention.

Referring now to the drawing in detail, I have shown an underground storage cavern 10 which includes, by way of illustration, a plurality of rooms 11a, 11b in the form of parallelepipeds, each room being connected at.

the lower portion thereof toa tunnel 12 and at the upper portion thereof to a tunnel 13. These tunnels communicate with a vertical shaft 14 extending to the surface of the earth. Another set of tunnels 12a and 13a are connected to the respective bottom and top portions of a plurality of silo-shaped excavated Caverns 15.

The top of the shaft is sealed by a head 17, and a downhole pump 18 is suspended in a sump 19 at the bottom of the shaft bya string 20 of tubing which extends through the head 17. This pump is used to withdraw the stored material from the cavern.

The cavern is lled through a drill hole 22 which communicates with a cavern 15. Another drill hole 23 communicates with the tunnel 13 and is provided with a pressure relief valve 24.

2,896,417` Patented July 28, 1959 The cavern illustrated herein, as more fully described in my copending application, Serial Number 314,541, tiled October 13, 1952, now abandoned, is one suitable type of cavern adapted for the practice of this invention. However, the system of this invention can also be utilized in various other types of excavated Caverns, and to caverns formed in salt or other types of soluble formations.

In accordance with the invention, vapors are Withdrawn from the cavern through a line 26, which communicates with head 17, either continuously or intermittently, and fed through a compressor 27 to a condenser 28 through which a cooling medium is circulated by lines 29 and 30. The condensed material passes through a line 31 to an accumulator 32 and is pumped back to the cavern through a valved line 33 `which communicates with the top of the shaft 14. It is preferred to spray the condensed material down shaft 14 to effect contact with the rising vapor and thereby improve the separation of light components from the heavier ones.

It will be apparent that the vaporization and subsequent condensation of the vapor produces a refrigeration effect within the cavern, and that the condensed material dissolves lighter components such as ethane or methane present in the gas or vapor space within the cavern. This substantially reduces the cavern pressure. In some cases, a heat exchanger is provided to exchange heat between lines 26 and 33.

If desired, light ends can be withdrawn from the accumulator 32 and passed through a valved line 35 to any suitable disposal, such as fuel. This removal `of light ends from the storage system causes a still further reduction i-n the cavern pressure.

In a cavern havin-g a capacity of about 260,000 barrels, propane is fed in at an average weekly input of 25,000 Ibarrels from a pipeline, the feed having a vapor pressure intermediate that of pure propane and propylene, say to 95 pounds per square inch gage at 55 F. The formation pressure is approximately 85 pounds per square inch gage while the vapor pressure within the cavern varies within -105 pounds per square inch gage due to concentration of light ends in the vapor space resulting from product withdrawal. By the compression and condensation of vapor from the cavern in the manner described herein, the pressure is readily reduced to the hydrostatic pressure of the formation ywhich in this instance is 80 to 85 pounds per square inch gage within the cavern, with the result that the surface tension effect of the Water in the formation at the wall surfaces, such as 15a, 11b, effectively prevents flow of any material into the surrounding formation out of the cavern or out of the surrounding formation into the cavern. This surface tension effect is Valuable in preventing leakage where the pressure difference between the formation and cavern vapor space is less than the pressure required to overcome the effect of surface tension.

It is a further advantage of the invention that operation of the present compression and condensation system denudes the effluent recovered from the cavern of the light materials, such as methane, ethane, nitrogen, oxygen and other impurities, so that the stored product withdrawn is actually purified, as compared to the product introduced into storage.

In one typical operation, 7,250 pounds per hour are Withdrawn from the cavern and compressed to 160 pounds per square inch gage at F. in the unit 27. The condensate from unit 28 has a pressure of 155 pounds per square inch gage at a temperature of 90 F. Vapor is removed from the accumulator 32 at a rate of 1500 pounds per hour for utilization as fuel, while 5,750 pounds per hour of material is returned to the cavern through the line 33. The composition at the compressor inlet is 2.7 percent methane, 9.9 percent ethane, 84.4

percent propane, 1.2 percent butane, 1.4 percent nitrogen and 0.4 percent oxygen. The vapor removed from the accumulator is 11.8 percent methane, 19.0 percent ethane, 66.0 percent propane, 2.3 percent nitrogen and 0.3 percent oxygen. All compositions are mol percentages.

Thus, by practice of the invention, the material in the cavern becomes somewhat denuded in ethane and lighter` gases, with resulting decrease in vapor pressure; the surface tension elect prevents leakage of stored material from tlhe cavern; and the vaporization and condensation cycle cools the stored liquid, `further reducing the pressure in the storage cavern.

While the invention has been described in connection with present, preferred embodiments thereof, it is to be understood that this description is illustrative only and is not intended to limit the invention.

I claim:

1. A method of operating an underground storage system which comprises introducing material into an underground storage cavern and withdrawing stored material therefrom, withdrawing vapors from said cavern, compressing said vapors, condensing the compressed vapors, returning the condensate to the storage cavern, and controlling the rate of withdrawal of vapors to the compressor in such fashion as to decrease the cavern pressure and thereby maintaining cavern pressure substantially equal to the formation pressure.

2. A method of operating an underground storage system which comprises introducing liquefied petroleum gas into an underground storage cavern and withdrawing stored liqueed petroleum gas therefrom, withdrawing vapors from said cavern, compressing said vapors, condensing the compressed vapors, separating a light gaseous fraction from said condensate and returning the condensate to the storage cavern, thus reducing the cavern pressure by the separation of the light gaseous fraction from the returned condensate.

3. A method of operating an underground storage system which comprises introducing material into an underground storage cavern and withdrawing stored material therefrom., withdrawing vapors from said cavern, compressing said vapors, condensing the compressed vapors, separating a light gaseous fraction from said condensate, returning the condensate to the storage cavern, and controlling the rate of withdrawal of vapors from the storage cavern to the `compressor so as to maintain the storage cavern pressure substantially equal to the formation pressure.

4. A method of operating an underground storage system which comprises introducing material into an underground storage cavern and withdrawing stored material therefrom through a vertical shaft tothe surface, withdrawing from the cavern vapors evolved from said material, compressing said vapors, condensing the compressed vapors, and spraying the condensate into the top portion of said vertical shaft, thereby to enhance the cooling and condensing action of said condensate and reduce the cavern pressure.

References Cited in the le of this patent UNITED STATES PATENTS Hunter June 12, 1956 

